Money should be used for God's work on Earth, and for nothing less.

When one thinks of money, one thinks of banknotes, or coins, or wealth, of expensive things, but all of this is merely the physical manifestation of a force that can be vitally manipulated and which, when possessed and controlled, almost mechanically brings with it the more material manifestations of money. It is a kind of power. It is a power to attract certain very material vibrations. By using the very fact of that power, its potency is increased. It is just like the effect that exercises have on the body: its potency is increased by its use. The power of money belongs to a world that has been created distorted; it belongs to the vital world. Sri Aurobindo also says so. Therefore, it has always been under the control of the asuric forces and must now be reclaimed from those forces. That's why people used to tell those who wanted to practice yoga or another discipline to stay away from money because it was (they said) devilish, asuric, or at least directly opposed to divine life. But the entire manifested universe is the Godhead itself and therefore belongs entirely to Him. It is in this perspective that Sri Aurobindo says that the powers of money belong to the Godhead. They must be reclaimed to give them back to Him. They have been under the influence of the asuric forces and must be reclaimed to place them at the disposal of the Godhead, so that He can use them for His work of transformation.

Money is a force, I've told you that before. It's a force of nature and it should be a medium of circulation, a force in motion, just as flowing water is a force in motion. It's something that can help us be productive, to organize things. It's a practical tool, because ultimately, it only serves to allow things to circulate freely and freely. That power should be in the hands of those who can best utilize it, namely those who have eradicated all personal desires and emotional ties. You should add to this a vision comprehensive enough to understand the needs of the earth, a knowledge complete enough to organize those needs and, equipped with these qualities, to utilize that power (money). If such people, moreover, possess a higher spiritual knowledge, they can use that power to gradually build on earth that which will be capable of manifesting divine power, strength, and grace. That power of money, of wealth, that financial capacity, which is, as it were, a curse, would then become a supreme blessing for the well-being of all.

The Mother, All Life is Yoga